"When she realised that it just wasn't possible for them to stay married, her focus was on keeping things amicable," the source continued.

In her divorce filing, Cavallari is hoping to become "the primary residential custodian" and assigning Cutler "reasonable periods of parenting time."

Kristin Cavallari and Jay Cutler in 2017. (Getty)

"She wants full custody of the kids, because she feels she is able to provide the most stable environment for them," source added. "Kristin is strong and confident. She is also an amazing mother. If Jay wants to break their deal about keeping things amicable, she is not scared of fighting for what she wants for their kids."

Meanwhile, another insider has claimed Cavallari was completely "blindsided" by Cutler's claims in his filing.

"She had hoped they could work things out more amicably and they were off to a good start before Jay pulled the trigger," a source told E! News on April 28.

Kristin Cavallari, Jay Cutler. (NBCU Photo Bank/NBCUniversal via)

In their divorce papers, Cutler listed "irreconcilable differences", while Cavallari cited both "irreconcilable differences" and "inappropriate conduct." The pair have also mentioned different dates for their formal separation; Cavallari noting April 7 as the date they split, and Cutler listing April 21.

"With great sadness, after 10 years together we have come to a loving conclusion to get a divorce," the statement read. "We have nothing but love and respect for one another and are deeply grateful for the years shared, memories made, and the children we are so proud of. This is just the situation of two people growing apart. We ask everyone to respect our privacy as we navigate this difficult time within our family."